Re-epithelializing pharmaceutical compositions comprising xanthan gum

ABSTRACT

The present invention relates to the use of xanthan gum as re-epithelializing agent and, in particular, to a pharmaceutical formulation comprising xanthan gum as a re-epithelializing active principle eventually mixed with hyaluronic acid. Said use and composition speed up and improve advantageously the formation of newly grown epithelium.

RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/512,521filed Oct. 25, 2004, which is a National Stage Under 35 U.S.C. § 371 ofPCT/IT03/00257, filed Apr. 24, 2003 claiming priority under Section119(e) to application number EPO 02425274.4 filed Apr. 30, 2002, thecontents of which are hereby incorporated by reference

FIELD OF THE INVENTION

The present invention relates to re-epithelializing pharmaceuticalcompositions especially for ophthalmic use.

BACKGROUND ART

It is well known that epithelial cells, for example in the cornea, maysuffer injuries caused by foreign bodies, such as abrasions, cuts andwounds (accidental, surgical, immunological etc), and postinfectiveulcers. Injuries of this sort generally require long wound healingperiods; cause much discomfort and often an imperfect wound closure.

SUMMARY OF THE INVENTION

The object of the present invention is a pharmaceutical composition thatcan accelerate re-epithelialization, especially of the corneal tissue,and is also well tolerated.

This goal is achieved using xanthan gum for the preparation of amedication for the treatment of epithelial wounds, as well as ofpharmaceutical compositions containing xanthan gum, as detailed in theclaims herewith annexed.

Other characteristics, and the advantages of the pharmaceutical topicalcomposition, as described in the present invention, will become apparentfrom the following description of some preferred embodiments offormulations of the pharmaceutical composition, which are presented forpurposes of illustration and are not intended to be construed aslimiting.

DETAILED DESCRIPTION OF THE INVENTION

A surprising experimental finding was the observation that xanthan gumshows a high re-epithelializing function, that is to say, it is able toaccelerate the formation of new epithelial cells at the level of thedamaged epithelial zone, as shown also in an in vivo experiment reportedlater in the present description.

Xanthan gum is a heteropolysaccharide with a molecular weight between3-7, 5×10 Da, produced through a process of fermentation by thebacterium Xanthomonas campestris.

The primary structure of xanthan is a branched chain, with a main chainof β (1→4)-D-glucose identical to cellulose wherein, a trisaccharidechain with a glucosidic link β (1→3), composed of acetylated mannose,glucuronic acid, and mannose is linked to every other second residue;finally, to each carbon C4 and C6 of the terminal unit of mannose amolecule of pyruvic acid is linked in a variable proportion of 25-50%,that completes the structure of the lateral chain of the polymer.

The available data suggests a single helix conformation (but a double ortriple helical structure cannot be ruled out) where the lateral chainsof the polymer tend to align with the main chain (with non covalent typeof interactions) protecting the glucosidic links present there. Theresult is a stiff rod-like structure that confers great stability to themolecule with an excellent protection from strong acids and bases, hightemperatures, freezing and thawing cycles, enzymatic attack, prolongedmixing, shear degradation, variations of ionic force and pH.

Consequently, on account of the structural properties just described,xanthan gum, in preformed gel form, makes it possible to carry outadequately the important function of mechanical protection.

Furthermore, following lot of experiments, it has been surprisinglyobserved that the admixture of xanthan gum with hyaluronic acid, as anactive principle of a re-epithelializing composition in a preparation asa preformed gel, causes an increase in the rate of re-epithelializing ofthe damaged epithelium and, in addition, promotes the reorganization ofthe newly formed epithelium that results in the formation of cellularlayer of superior quality.

In particular, wound-healing studies carried out under a scanningelectron microscope, revealed a surprising degree of epithelialorganization following a treatment with the pharmaceuticalre-epithelializing composition according to the invention, as will beexplained in detail.

It is well known that hyaluronic acid not only favors cellularproliferation but also stabilizes the basal layer of the epitheliumstimulating the production of lamina and fibronectin.

In any event, when xanthan gum and hyaluronic acid are used as a mix intheir capacity as re-epithelializing agents, they have a surprisingsynergic effect.

Hyaluronic acid is an high molecular weight polysaccharide withpolyanionic features, high capacity to retain water, viscous,bioadhesive and pseudoplastic properties with no evidence of tixotropy.Its primary structure consists of β (1→4) disaccharide blocks eachconstituted of D-glucuronic acid and N-acetyl-D-glucosamine linkedtogether through a β (1→3) bond.

In view of the observations previously described, a further embodimentof the present invention is to provide topical re-epithelializingpharmaceutical compositions in preformed gel consisting essentially ofxanthan gum as active principle, eventually mixed with hyaluronic acid,and pharmacologically accepted additives.

The percentage of xanthan gum relative to the total volume of thepreformed gel is preferably between 0.7% to 5%, more preferably between0.8% and 3%, and more highly preferably between 0.9% and 1.5%.

The excipients are chosen among isotonic agents, buffers, solvents orvehicles, antioxidants, pH adjusting and similar.

In particular, the possible isotonic agents of the composition of theinvention may be ionic, such as NaCl, KCl or non-ionic, for exampleglycerol, mannitol or a mix thereof.

Possible buffers may be those commonly used for instance in ophthalmicformulations such as phosphate or borate, acetate, a mix of thesebuffers such as citrate/phosphate, or even buffers not frequently usedin the ophthalmic field, such as Tris.HCl, or based on histidine orarginine.

Therefore, the composition of a preformed gel with xanthan may be abalanced saline solution, or otherwise, o saline composition notnecessarily balanced because of the presence of ions of Ca⁺²e Mg⁺².

Possible antioxidants include sodium citrate, ascorbate or sulfate.

Possible pH adjusting are organic or inorganic acids or bases with theirrespective acid and basic salts.

Possible solvents or vehicles are water or a mixture of water/oil.

It has been observed that when salts are added to a compositioncontaining >0.25% xanthan, there is an increase of viscosityproportional to the concentration of xanthan and of the added salts,although a viscosity plateau is reached, for example, with as little as0.1% of NaCl. Therefore, xanthan behaves differently toward thevariations of ionic force than other polyelectrolytes, toward which thepresence of salts (that decreases the degree of hydration and repulsionbetween chains) promotes intermolecular interaction and a molecularcollapse from a random coil (with a higher viscosity) to a compact coilstructure (with a lower viscosity). In xanthan solutions the addition ofsalts decreases the degree of hydration and the charge repulsion betweenthe carboxylate anions of the lateral chains of the molecule, whichconsequently stabilizes the stiff rod-like conformation and promotes astronger and more rigid three-dimensional network that increasesviscosity (about twofold at 0.1% of NaCl for 1% xanthan) and significantyield-value, that in general render the solutions of the polymer moreprotected against factors such as thermal treatment, attacks from acidsand bases, prolonged mixing, etc.

In solution, the single helixes tend to associate forming a complexordered meshwork of rigid molecules held together mainly by weak Van derWaals forces. The effect of the distinctive and unique structure ofxanthan in solution is, already for moderate concentrations (1-2.5%), agel-like consistency with significant yield stress values (hence,excellent ability to favor the formation of suspensions and emulsions)and good viscosity.

Taken together, the properties thus far examined, along with the lowtoxicity, bioadhesiveness, and compatibility with the most commonexcipients and available commercial packaging render xanthan gumadvantageously suitable also as delivery system as well as a protectiveagent on purely mechanical grounds.

As mentioned before, an additional embodiment of the present inventionmay include hyaluronic acid.

Specifically, the quantity of hyaluronic acid present in saidcomposition ranges from 0.01% to 1% of the total volume of the preformedgel, preferably from 0.05% to 0.5%, better still from 0.1% to 0.4%.Hyaluronic acid is present as a salt. Possible counter ions may be, forexample, sodium, potassium, calcium or magnesium.

In yet another embodiment of the present invention there-epithelializing pharmaceutical composition may include, aside fromthe admixture of xanthan gum and hyaluronic acid as re-epithelializingagents, one or several pharmacological agents chosen amongantiinfective, antiinflamatory, anesthetizing and mydriatic agents.

The invention is further disclosed by means of the following nonlimiting examples of same formulations.

FORMULATION 1 Components Quantity Function Xanthan gum 1.0000 g Activeprinciple, re-epithelializing Sodium chloride 0.3500 g Isotonic agentSodium phosphate, 0.3638 g Buffer dibasic•12H₂O Sodium phosphate 0.0354g Buffer monobasic•H₂O Glycerol 1.0000 g Isotonic agent Purified waterq.s. to  100.0 ml Solvent

FORMULATION 2 Components Quantity Function Xanthan gum 1.0000 g Activeprinciple, re-epithelializing Sodium chloride 0.3500 g Isotonic agentPotassium chloride 0.1500 g Isotonic agent Magnesium•chloride 0.0120 gIsotonic agent 6H₂O Calcium chloride•2H₂O 0.0084 g Isotonic agent Sodiumphosphate 0.0890 g Buffer dibasic•12H₂O Sodium phosphate 0.0069 g Buffermonobasic•H₂O Sodium citrate•2H₂O 0.0590 g Buffer/antioxidant Glycerol1.0000 g Isotonic agent Purified water q.s. to  100.0 ml Solvent

FORMULATION 3 Components Quantity Function Hyaluronic acid sodium salt0.1500 g Active principle, re-epithelializing Xanthan gum 1.0000 gActive principle, re-epithelializing Sodium chloride 0.3500 g Isotonicagent Potassium chloride 0.1500 g Isotonic agent Magnesium chloride•6H₂O0.0120 g Isotonic agent Calcium chloride•2H₂O 0.0084 g Isotonic agentSodium phosphate dibasic•12H₂O 0.0890 g Buffer Sodium phosphate 0.0069 gBuffer monobasic•H₂O Sodium citrate•2H₂O 0.0590 g Buffer/antioxidantGlycerol 1.0000 g Isotonic agent Purified water q.s. to  100.0 mlSolvent

FORMULATION 4 Components Quantity Function Hyaluronic acid sodium salt0.1500 g Active principle, re-epithelializing Xanthan gum 1.0000 gActive principle, re-epithelializing Sodium chloride 0.3500 g Isotonicagent Potassium chloride 0.1500 g Isotonic agent Magnesium chloride•6H₂O0.0120 g Isotonic agent Calcium chloride•2H₂O 0.0084 g Isotonic agentTris base 0.2425 g Buffer HCl 1N q.s. to pH 7.4-7.6 Buffer Sodiumcitrate•2H₂O 0.0590 g Buffer/antioxidant Glycerol 0.5000 g Isotonicagent Purified water q.s. to  100.0 ml Solvent

FORMULATION 5 Components Quantity Function Netilmicin sulfate 0.4550 gActive principle equivalent to Netilmicin base 0.3000 g Sodiumhyaluronate 0.1500 g Active principle, re-epithelializing Xanthan gum1.0000 g Active principle, re-epithelializing Sodium chloride 0.8700 gIsotonic agent Sodium hydroxide 1M q.s. to pH = 7.00-7.6 pH adjustingPurified water q.s. to  100.0 ml Solvent

FORMULATION 6 Components Quantity Function Netilmicin sulfate 0.4550 gActive principle equivalent to Netilmicin base 0.3000 g Sodiumhyaluronate 0.1500 g Active principle, re-epithelializing Xanthan gum1.0000 g Active principle, re-epithelializing Sodium phosphate 0.5000 gBuffer dibasic dodecahydrate. Sodium phosphate 0.1465 g Buffer monobasicmonohydrate Sodium citrate dihydrate 2.1000 g Buffer/antioxidantPurified water q.s. to  100.0 ml Solvent

FORMULATION 7 Components Quantity Function Netilmicin sulfate 0.4550 gActive principle equivalent to Netilmicin base 0.3000 g Sodiumhyaluronate 0.1500 g Active principle, re-epithelializing Xanthan gum1.0000 g Active principle, re-epithelializing Tris base 0.2425 g BufferHCl 1M q.s. to pH 7.4-7.6 Buffer Sodium citrate dihydrate 2.1000Buffer/antioxidant Purified water q.s. to  100.0 ml Solvent

FORMULATION 8 Components Quantity Function Netilmicin sulfate 0.4550 gActive principle equivalent to Netilmicin base 0.3000 g Sodiumhyaluronate 0.1500 g Active principle, re-epithelializing Xanthan gum1.0000 g Active principle, re-epithelializing Tris base 0.2423 g BufferHCl 1M q.s. to pH 7.4-7.6 Buffer Sodium chloride 0.7000 g Isotonic agentPurified water q.s. to  100.0 ml Solvent

FORMULATION 9 Components Quantity Function Dexamethasone disodium 0.1500g Active principle phosphate Xanthan gum 1.0000 g Active principle,re-epithelializing Sodium phosphate 0.5000 g Buffer dibasic•12H₂O Sodiumphosphate 0.1465 g Buffer monobasic•H₂O Sodium citrate•2 H₂O 2.1000 gAntioxidant Purified water q.s. to  100.0 ml Solvent

FORMULATION 10 Components Quantity Function Dexamethasone disodium0.1500 g Active principle phosphate Netilmicin sulfate 0.4550 g Activeprinciple equivalent to Netilmicin base 0.3000 g Xanthan gum 1.0000 gActive principle, re-epithelializing Sodium phosphate 0.5000 g Bufferdibasic•12H₂O Sodium phosphate 0.1465 g Buffer monobasic•H₂O Sodiumcitrate•2H₂O 2.1000 g Antioxidant Purified water q.s. to  100.0 mlSolvent

In general, in the compositions of the invention, glycerol displays adispersing action towards xanthan gum, preventing the formation ofclumps and lumps during the dispersal phase of the polymer in H₂O.

A general description of a procedure for the preparation of apharmaceutical composition in accordance with the present invention willnow follow. By way of illustration, the formulation prepared is for 100ml/g of product.

Procedure for the Preparation of a Preformed Re-epithelializing Gel

In a volume of purified water of about 50 ml all the additives of theformulation are added and dissolved, adding each component after thepreceding one has been completely dissolved.

If the composition requires it, a predetermined quantity of one or moreof the pharmacological agents listed above is added to the solutionuntil said pharmacological agent(s) is/are completely dissolved ormixed.

Separately, one gram of xanthan gum is added to 50 ml of water and isdispersed on the surface of the liquid, without stirring, to avoid theformation of lumps. Alternatively, the dispersion may be homogenizedwith a paddle stirrer or a homogenizer so as to accelerate the processwhile avoiding the formation of lumps. If the composition requires it,hyaluronic acid is also dispersed in this phase.

The homogeneous dispersion is then autoclaved until a minimum F0=15valid for the sterility is obtained (lethality, expressed in terms ofequivalent of time in minutes at a 121° C. temperature with reference tothe killing of microorganisms during the process of steamsterilization).

A this point, the solution of the additives sterilized thorughfiltration (if a suspension sterilize in suitable manner) is asepticallyadded to the xanthan gum dispersion and stirred for about 1 hr. at aspeed that will allow for smooth mixing without excessive turbulence,until a homogeneous gel is obtained.

Finally, the gel may be aseptically distributed in the appropriatecontainers.

To illustrate the efficacy of the main compositions of the invention,two experiments will be describe that were carried out to verify, in anin vivo re-epithelializing model, the effect of 2 preformed gelsaccording to the aforesaid formulations—one (Formulation 2) containingonly xanthan gum (XNT) and another (Formulation 3) containing bothxanthan gum and hyaluronic acid (EPG)—in comparison to a solutioncontaining only 0.15% sodium hyaluronate and salts (EYP) and a salinesolution with no polymers (SOL).

Re-epithelialization Efficacy

The difference between the two experiments lies in the fact that thefirst is designed to assess the dynamic and quantitative aspects ofre-epithelialization and the second to assess the morphological andqualitative aspects of re-epithelialization following treatment with thevarious formulations. In the first experiment a confocal ophthalmoscope(CSLO) was used to follow the re-epithelialization rate and in thelatter a scanning electron microscope (SEM) was used for theultrastructural analysis.

For each experiment New Zealand albino rabbits, subdivided in 6treatment groups according to what is described in the next twoparagraphs, were used

Animals

Male New Zealand albino rabbits (Charles River Italia), medium weight2.400 Kg, were used.

The animals were allocated in animal rooms maintained in standardconditions of humidity (50%±10% RH) and temperature (19±2° C.) withalternating cycles of artificial light (12 hours darkness/light). Theanimals were fed and allowed water ad libitum.

Treatment Scheme and Regimen

After checking the eyes of the animals to exclude eventualophthalmological pathologies, the animals were assigned to six differenttreatment groups according to the following scheme:

Animals used during the different observation and treatment times

T₀ T_(24 h) T_(48 h) T_(72 h) T_(96 h) Control 4 — — — Untreated wound 44 4 4 4 EPG 4 4 4 4 4 XNT 4 4 4 4 4 EYP 4 4 4 4 4 SOL 4 4 4 4 4 LegendControl: animals with intact cornea not pharmacologically treated.Untreated wound: animals with corneal wound not pharmacologicallytreated EPG, XNT, EYP, SOL: animals with corneal wound treated with thedifferent formulations

All the tested substances were administered 5 times a day until the endof the experiment.

Experimental Model

The animals were anesthetized by an i.m. injection of ketamine (37.5mg/kg b.w.) and xylazine (10 mg/kg b.w.), and with oxybuprocaine (1drop/eye).

The corneal wound was executed using an Algerbrush with a 1 mm tip. Withthe aid of a sterile parafilm mask, with a 6 mm hole at the center, acircular area was de-epithelialized. The eye was immediately washed withsterile BBS to remove cell debris and the treatment was performed.

In time course the rabbits were evaluated at 0, 24, 48, 72 and 96 hourswith a CLSO coupled to an image-processing system, or they weresacrificed for SEM analysis (0, 24, 48, and 72 hours).

The research method and results of each experiment are describedhereafter.

CLSO Experiment

The eyes of the rabbits of each treatment group were treated with a 25μl solution of 0.5% sodium fluorescein. After 2 minutes the excess offluorescein was washed away with a physiological solution. The sedatedrabbits were then examined through CLSO. This system detects thefluorescent signal that originates from the epithelium lacking damagedzone and measures quantitatively the damaged area through animage-processing system.

Results

The CLSO analysis revealed that the wound heals spontaneously after 72hours in all the treated groups.

The group treated with the formulation containing only xanthan gum asactive principle (XNT) showed an accelerated re-epithelializationprocess already 24 hours after the treatment. The wound's closure was atleast 30% more advanced than in the groups “Untreated wound”, EYP andSOL. A higher re-epithelialization rate (50% higher than the othergroups) was observed 48 hours after the treatment in both the grouptreated with xanthan gum only (XNT) and the group treated with xanthangum mixed with hyaluronic acid (EPG). There were no observed differencesbetween the group treated with only sodium hyaluronate (EYP) and thegroups SOL and “untreated wound”.

SEM Experiment

At predetermined times (0, 24, 48, 72 hours from the beginning oftreatment) the animals of the different treatment groups were sacrificed(Tanax i.v.). Rapidly following the sacrifice the bulb was enucleatedand the corneas excised and immediately fixed with 2% glutaraldehydeduring 24 hours. Following fixation the corneas were processed for SEManalysis.

Results

All the corneas processed for observation immediately after cornealde-epithelialization (T₀) exhibit wounds with sharp raised margins andnaked stroma. The controls (intact corneas) exhibit an homogeneousepithelium with a good degree of cellular differentiation, and a normalpresence of “holes” (circumscribed areas lacking microvilli that arepresent on the surface of the epithelial cells with probablecommunication functions), serrated cellular contacts and numerousmicrovilli, presence of superficial epithelium with the typical mosaicaspect that reflects the different maturation stages (dark, medium lightand light cells).

T24 Ore

Twenty four hours after the beginning of the experiment, the corneas ofthe group “Untreated wound” exhibit a de-epithelialized area with anentirely naked stroma, with the margin of the epithelium lacking zonesharp but hardly raised. All the newly formed cells present at themargins of the “wound” or slightly outside show few microvilli, and arenot clearly differentiated into dark, medium and light.

The margins of the wounds of the corneas of the SOL group are similar tothose of the preceding group, but the newly formed cells are moredifferentiated, with the presence of the three differentiation stages,and more profuse microvilli. Moreover, the cells are centripetallyelongated, in contrast to the samples taken from the “Untreated wound”group, where the oblong shape is less evident.

In the corneas of the EYP group the margin of the epithelium-deprivedzone is flattened and circumscribed by a ring of differentiated newlyformed cells with a centripetally elongated aspect.

The corneas of the XNT group have an aspect to a large extent similar tothose of the EYP group.

The corneas in the EPG group exhibit a flattened wound margin with cellswith microvilli more numerous than in the other treatment groups. Thenewly formed cells exhibit a fair number of “holes”.

T 48 Ore

The corneas of the “Untreated wound” group observed after 48 hours atthe lowest magnification, exhibit a quite disorganized de-epithelializedzone, with marked and indented margins, and newly formed cells withpartially enlarged junctions. A small number of cells are elongated andthe small number of microvilli is short and distributed uniformly withno differentiation between light, medium and dark cells.

The samples of the SOL group also exhibit a de-epithelialized zone withquite irregular contours with marked margins, although the newly formedcells appear more differentiated, and the microvilli more numerous withvirtually normal shape. The edges of the cells bordering the margins ofthe re-epithelialized zone are enlarged and in some cases raised.

The corneas of the EYP group re-epithelialized similarly to the corneasof the other groups. However, the contours of the de-epithelialized zoneremain irregular, even if the degree of differentiation, thedistribution and the quality of the microvilli of the newly formed cellsis good.

The samples from the XNT treatment group exhibit irregular woundcontours, but the state of the newly formed epithelium is notably betterthan that of the other groups. The new epithelium zone at theproximities of the wound margins presents a ring of centripetallyelongated cells. Moreover, the degree of cellular differentiation, aswell as the cellular contours are good, although zones where the cellsappear raised in part persist. The microvilli are normal and numerous.

The organization of the samples of the EPG treatment group is similar tothat of groups EYP and XNT. However, the edge of the wound, as in theprevious observation time, is still flat. Consequently, the newly formedzone with centripetally oriented cells is larger, and in general, evenat the lowest magnification, the aspect of the de-epithelialized zone ismore uniform.

T 72 Ore

After 72 hours of treatment all the groups exhibit a healed wound,although small, spottily-distributed areas barren of cells and withenlarged junctions persist. This phenomenon is part of the normalre-epithelialization process and is caused by the continuousrearrangement of the newly formed epithelium.

The differences between the groups lie in the organization of the newlyformed epithelium. In fact, in the “Untreated wound” group theepithelium appears uniform because of the presence of short and scantmicrovilli that give the epithelium a “pasty” appearance. Thus, thetypical dark, medium and light cell differentiation is not present,except in the zones of newly formed epithelium more distant from thecenter, probably because in those zones the cellular turnover hasreturned to normal, while at the center cellular multiplication is stillchaotic.

A certain degree of epithelial organization is exhibited by the SOLsamples. In fact, even at the central zone, re-epithelialized later, ahint of differentiation is present, and in comparison to the corneas ofthe “Untreated wound” group, the microvilli are more numerous and“not-pasty”.

The differences between the groups treated with the products containingbiopolymers persist even at 72 hours, although the corneas treated withEPG are better that those treated with XNT, and the latter are betterthan those of the EYP group. In general the aspect of the corneastreated with EPG is similar to that of the controls (intact corneas),with numerous and long microvilli, a fair number of holes uniformlydistributed in the cellular layer, and a good representation of cells atthe diverse differentiation stages.

According to what has been described so far, the re-epithelializingpharmaceutical composition in preformed gel form accelerates thereconstruction of the damaged epithelium.

Moreover, said composition advantageously favors the reorganization ofthe epithelium and consequently increases the adhesion and stability ofthe new epithelium in the underlying connective tissue.

A further advantage of the composition, according to the presentinvention, is its formulation as a preformed gel as a consequence ofwhich the re-epithelializing pharmaceutical composition also performs amechanically protective function.

Preferably, when the composition of the invention includes the sodiumsalt of hyaluronic acid, its formulation exhibits extremely favorablecharacteristics for a product of topical use.

In particular, the consistency is that of an almost transparent, lightcream colored, pleasant to the touch, non-sticky, easily spreadable andabsorbed soft gel. The sensations upon instillation are similar: thepreparation does not burn, the “blurry vision” sensation is very limitedo non-existent while that of freshness and lubrication of the eyepersists. Additionally, the product is easily administered both in termsof release from the container (ease of drop formation and delivery) anddistribution of the drops on the ocular surface.

Furthermore, it was surprisingly observed that hyaluronic acid, althoughpresent in water at concentrations almost seven times lower than that ofxanthan gum, has notable stabilization ability with respect to theconformation of the latter.

In fact, the viscosity of xanthan gum solutions without salts decreasein about 30% following thermal treatment.

On the contrary, the viscosity of xanthan gum solutions and hyaluronicacid sodium salt decreases only in 10-15% after thermal treatment.

In particular, the study of the Theological characteristics of theproduct has given the following results.

As an illustration, the viscosity/shear rate (η/γ) diagram of acomposition consisting of 1% xanthan gum+hyaluronic acid was studied andcompared to a composition of 1% xanthan+saline solution (BSS) and 1%xanthan+H₂O.

The rheological profile of the complete product presents very high η(viscosity) and well-defined shear stress at low γ, and therefore, goodstrength, reticule consistency, and retention at the site ofapplication. Viscosity (η) decreases rapidly as shear rate increaseswith a high degree of pseudoplasticity that confers good spreadabilityand distribution to the system at the application site, and gives theuser a comfortable sensation. The η/γ curve obtained by graduallyincreasing the shear rate coincides with that of the reverse path,obtained by gradually diminishing it; therefore, the system presents notissuetropy and reacquires its structure instantaneously upon cessationof the shear stress.

In particular for ocular applications, this translates itselfadvantageously in the recovery of the structure and viscosity of theproduct between blinks consequently increasing the time of cornealcontact.

As may be assessed from what has been described herewith, are-epithelializing pharmaceutical composition according to the presentinvention answers to the needs mentioned in the introductory section andovercomes the shortcomings of the current state of the arts.

Obviously an expert in the field, in order to satisfy contingent andspecific requirements may introduce numerous modifications andvariations to the above-described composition, without departing fromthe scope of the invention as defined by the following claims.

1. Method for the treatment of epithelial wounds, which comprisesadministering an effective amount of xanthan gum.
 2. The methodaccording to claim 1, wherein xanthan gum is in admixture withhyaluronic acid.
 3. The method according to claim 1, wherein xanthan gumis administered in association with a medicament chosen amongantiinfectives, antiinflamatories, anesthetics, and mydriatics.
 4. Themethod according to claim 1, wherein said epithelial wound is a wound ofthe corneal epithelium.
 5. The method according to claim 1, involvingpromoting the proliferation of epithelial cells. 6-23. (canceled) 24.The method according to claim 2, wherein xanthan gum is administered inassociation with a medicament chosen among antiinfectives,antiinflamatories, anesthetics, and mydriatics.